In fracturing subterranean formations from typical underground cased wells, the point of initiation of the fractures in the well may be relatively precisely located because the fracture can only initiate at the location where the casing has been perforated. However, it is sometimes necessary or desirable to fracture a subterranean formation from a non-cased, or open hole, completed well section. In those scenarios, one particular challenge is to be able to initiate the fracture at a desired location in the well.
In open hole scenarios, the fracture may occur at an unpredictable location in the well bore, such as may be due to the effects in the open hole caused by applied fluid pressure in the well. For example, when there is no casing or other fluidly impermeable barrier between pressurized well fluid and the exposed rock that forms the wall of the open hole, the rock could crack and fracture at an undesirable or intermediate location. The inability to control or pinpoint the fracture initiation location in open hole wells may be particularly important, for example, when attempting to form multiple fractures in a subterranean formation from a non-vertical section of an open hole well. As used herein, a “non-vertical” well may be a horizontal, lateral, inclined, deviated, directional or similar well.
Various techniques have been proposed for isolating the fracture initiation location in an uncemented lined well. For example, one current system utilizes one or more packer and sliding sleeve for segmenting a selected leg of a well bore. Using mechanical isolation, this equipment allows intervals of a horizontal well section to be segregated and stimulated separately. However, few techniques are believed to exist for open hole wells. One system utilizing a hydrojetting tool for jetting fluid through a nozzle at high pressures has been proposed for fracturing the formation where the fluid jet impacts the borehole wall. Positioning the jetting tool at the desired location allegedly results in the initiation of a fracture at that location.
Presently known techniques for isolating the fracture initiation location in an uncemented lined well may involve the use of specialized equipment that may be large and complex, costly to manufacture and utilize, and/or subject to sticking in the well and failure. While open hole completions typically require non-costly or complex equipment to be installed in the producing section of the well, the effectiveness and/or efficiency of proposed open hole fracturing techniques is questionable. For example, when the aforementioned hydrojetting tool is used to create a fracture, pressure must be maintained in the well bore annulus. Any weakness in the rock along the bore hole wall may result in the formation of an unexpected or undesirable fracture.
It should be understood, however, that the above-described examples, features and/or disadvantages are provided for illustrative purposes only and are not intended to limit the scope or subject matter of the claims of this patent or any patent or patent application claiming priority hereto. Thus, none of the appended claims or claims of any related patent or patent application should be limited by the above discussion or construed to address, include or exclude the cited examples, features and/or disadvantages, except and only to the extent as may be expressly stated in a particular claim. Further, the above exemplary disadvantages should be evaluated on a case-by-case basis.
Accordingly, there exists a need for methods useful for allowing the formation of fractures in a subterranean formation from an open hole portion of a well bore having one or more of the following attributes, capabilities or features: allows the formation of multiple fractures from a non-vertical open hole well portion; allows the formation of multiple distinct fractures from a non-vertical open hole well portion; allows the formation of multiple fractures from a horizontal open hole well portion; allows relatively precise location of fractures in an open hole well portion; utilizes an easily removable coating that is substantially impermeable, strong and/or coherent, essentially eliminates the effects of poroelasticity upon the formation under the coating regardless of the nature or type of hydrocarbons produced therefrom and in a wide range of temperatures, may be 100% soluble, or any combination thereof; protects each fracture from damage caused by subsequent formation fracturing; includes a non-damaging plug placed across the fracture and along a portion of the well bore proximate thereto to isolate the fracture from any subsequent fracturing operations; includes a proppant plug that does not substantially invade the fracture, does not impair conductivity of the fracture, is easy to clean out, or a combination thereof; may be implemented with the use of coiled tubing or a jointed pipe string; does not require additional, complex or costly equipment; is effective, cost efficient, reliable and/or easy to implement.